Field of the Invention
The invention concerns a compact flow control valve capable of providing long service life in a very hostile environment. The valve is a mono or dual coaxial slider valve capable of controlling two different functions sequentially, at least one of the functions being controlled progressively.
Description of the Related Art
Valves are used to control the flow of gases. A particularly harsh environment for valves is the turbocharger. Although a variety of valves has been developed and used with varying degrees of success in the past, as engine requirements evolve, greater demands are placed on the valves.
For example, to improve vehicle fuel economy, it is desired to keep the aerodynamic frontal area of the vehicle as small and streamlined as possible. The compactness of the engine compartment reduces the freedom for locating and orienting auxiliary equipment such as turbocharger actuators. To optimize use of space, the valve should be small, light weight, and freely assembled in any orientation, and it would be particularly advantageous for the valve to control more than one function.
Turbochargers are driven by exhaust gases. The outside of the turbine housing faces ambient air temperature while the volute surfaces contact exhaust gases ranging from 740° C. to 1050° C., depending on the type of combustion in the engine. Valves operating in exhaust gases are exposed to high temperatures and corrosive acids as well as soot particles which may accumulate on internal surfaces of the turbocharger. Any valve must be capable affording a tight seal and controllable opening, without corrosion or jamming due to soot or oil buildup. It would be advantageous to design a valve that is less susceptible to jamming.
The back-pressure within the turbine system can be in the region of up to 500 kPa. It would be advantageous to improve the design of a valve such as a wastegate so that it can be controlled with high precision, with minimal actuation force, without being adversely affected by high system pressures.
In a wastegated turbocharger, the turbine volute is fluidly connected to the turbine outlet downstream of the exducer by a bypass duct. Flow through the bypass duct is controlled by a valve known as a wastegate. To operate the wastegate, an actuating or control force must be transmitted from outside the turbine housing, through the turbine housing, to the wastegate inside the turbine housing. For example, a wastegate pivot shaft may extend through the turbine housing. Outside the turbine housing, an actuator is connected to a wastegate arm via a linkage, and the wastegate arm is connected to the wastegate pivot shaft. Inside the turbine housing, the pivot shaft is connected to the wastegate. Actuating force from the actuator is translated into rotation of the pivot shaft, pivoting the wastegate inside the turbine housing. The wastegate pivot shaft rotates in a cylindrical bushing, or directly contacts the turbine housing. Because the exhaust gas is under pressure, and because an annular gap exists between the shaft and the bore of the bushing, in which the shaft is located, an escape of hot, toxic exhaust gas and soot from the pressurized turbine housing is possible through this clearance. This is a source of hydrocarbon emissions that should be reduced. Gas and soot leakage from within a turbocharger to the ambient clean air surrounding a turbocharger is not permitted by engine manufacturers. A better containment of the turbocharger exhaust gasses is desirable.
Further, in conventional wastegate, the pressure at which the wastegate begins to open (the “lift off pressure”) is critical to the operation thereof. The wastegate must be very carefully set when the pneumatic actuator and wastegate assembly are assembled to the turbocharger. The precise actuator can pressure, at which the diaphragm begins to move, is dependent upon the preload of the spring used. Variation in the manufacturing tolerances of springs means that variations in spring rate from one spring to the next is likely, and it is necessary to calibrate each turbocharger, individually, to determine the lift off pressure. It is desired to have a valve such as a wastegate that is precisely controllable and free of these manufacturing variations.
Attempts have been made to use a single actuator for dual functions. U.S. Pat. No. 4,893,474 teaches an exhaust gas driven turbocharger provided with a single pneumatic actuator which controls both a pivoting vane which varies the flow area or aspect ratio of the exhaust gas inlet passage to the turbine, and also controls a wastegate valve. A linkage mechanism including a preloaded spring and a bellcrank lever actuates levers controlling the wastegate valve and the pivoting vane. This design is however rather complex and thus liable to fail, is not compact, and requires multiple valves to control the multiple functions.
U.S. Pat. No. 8,196,403 (Caterpillar) teaches a turbocharger having a balance valve, a wastegate, and an actuator common to both the balance valve and the wastegate valve. A valve assembly may be associated with turbine to regulate a pressure of exhaust within EGR circuit. Valve assembly may include, among other things, a balance valve, a wastegate valve, and a common actuator. Balance valve may be configured to selectively allow exhaust from first volute to pass to second volute. Wastegate valve may be configured to selectively allow exhaust from second volute to bypass a turbine wheel of turbine. Common actuator may be controlled to move both balance valve and wastegate valve between flow passing and flow blocking positions. Valve assembly may be integral with turbine and at least partially enclosed by a valve housing that mounts to a turbine housing of turbine. The system however employs multiple flap valves which require substantial actuator force to close. The rotary shafts can become clogged and jam.
There is a need not only to be able to control multiple functions with a single actuator, but also to be able operate multiple functions with a single valve or valve assembly (hereafter valve). Further, there is a need for a valve which can be operated with minimal actuation force. Finally, there is a need for a valve which does not slam into end positions.